Photonic integrated circuits based on linearly coupled waveguide arrays

Abstract

Photonic integrated circuits (PICs) are a promising route towards the next generation of classical and quantum information technologies. The main challenges before their widespread implementation are achievements of the competitive footprint, speed and number of simultaneous operations. This translates into requirements for miniaturization, broad bandwidth and extensive spatial and wavelength multiplexing. Current PIC designs commonly rely on directional couplers for operations and waveguides for information transfer. However, their miniaturization potential is limited by the trade-off between losses and bend radii in the former case and the crosstalk between densely packed waveguides in the latter case. On the other hand, operationally successful nanophotonic inverse designs are achieved only with substantial time and energy resources per device [1,2]. Here, we present and discuss an innovative solution for design of PICs which utilizes the linear crosstalk between waveguides [3]. We demonstrate construction of interconnects, couplers, interferometers, filters and dichroic splitters [4-6]. As the only fundamental assumption is the linear coupling between waveguides, these designs are applicable to all photonic fabrication platforms. We show components in glass, silicon nitride and silicon-on-insulator, and offer strategies for optimization of their footprint and bandwidth. The concept has been experimentally validated by fabrication of equal power splitters in glass. The optimization capability was proven by the achieved negligible insertion loss, large bandwidth and footprint scalability [7]. The proposed PICs are highly cost effective. Our simple semi-analytical design algorithm ensures efficient design, 20-100 times faster than the competing nanodesigns [1,2], and production realizable by any waveguide fabrication technique. Finally, we show that the quantum walk through the proposed linearly coupled waveguide arrays offers numerous possibilities for exploitation of qudits and construction of quantum logic gates.